An estimated 15–20 percent of couples worldwide are affected by infertility. Of those, approximately 30–40 percent are infertile due to male factors, including sperm motility. Another 20 percent are infertile due to a combination of male and female factors.

Healthy sperm motility is defined as sperm with forward progressions of at least 25 micrometers per second. If a man has poor sperm mobility, it’s called asthenospermia or asthenozoospermia. There are different types of sperm motility issues, including:

slow or sluggish progressive motility

non-progressive motility, which is defined as anything less than 5 micrometers per second

no mobility

Sperm speed and gender: Fact or fiction?

It’s long been thought that sperm with Y chromosomes, or “boy” sperm, swim faster than sperm with X chromosomes, known as “girl” sperm. Studies have proven that this is a myth, however, and there is no noticeable difference in motility or speed between X and Y sperm.

The exact cause for low sperm motility can vary. Some men may have a genetic cause, while others may have an undiagnosed medical condition. Lifestyle and environmental factors also play a big role in sperm motility. Smoking, for example, has been linked to decreased sperm motility, especially if the man smokes more than 10 cigarettes per day. Men who work in the military or have jobs that include painting, driving, or repeated trauma to the pelvic area may be at risk for work-induced infertility.

A condition called varicocele occurs when veins inside the scrotum become enlarged. This has also been linked to decreased sperm motility.

Low sperm motility may also be due to a disorder in the male accessory sex gland secretion, which leads to the glands emptying more slowly.

Sperm motility can be tested through a routine semen analysis. For the test, you’ll need to provide at least two semen samples. These are usually obtained by masturbation at a doctor’s office or testing facility. It’s also possible to obtain a sperm sample by having sex with a condom or withdrawing to obtain the sample. The sample must be kept at room temperature and delivered to the facility within 30 to 60 minutes. If less than 40 percent of your sperm are motile, your considered to have low sperm motility.

In addition to sperm motility, your doctor can also use a semen analysis to test:

Some supplements may also help improve sperm motility. For example, one study found a 52 percent increase in sperm motility in men who took a daily supplement of 200 micrograms of selenium along with 400 units of vitamin E for at least 100 days in a row. Speak to your doctor before taking supplements, and be careful about where you buy them. Supplements are not regulated, so you should only buy them from reputable vendors.

If the cause of the sperm mobility issue is a medical problem, such as low hormone levels or varicocele, medication such as follicle-stimulating hormone or human chorionic gonadotropin may help. In some cases, your doctor may recommend surgery.

Many factors can affect male fertility. If the sperm is otherwise healthy, pregnancy with low sperm motility can occur. Using a reproductive technology such as in vitro fertilization or intrauterine insemination (IUI) can help increase the chance of pregnancy. This is because they bypass the need for the sperm to swim on their own.

Talk to your doctor if you’ve been trying unsuccessfully to conceive for 12 or more months. Your doctor can test you and your partner to determine if there are any health conditions affecting fertility. Your doctor will then determine next steps.